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Home My WebLink AboutSW4240801_Stormwater Narrative_20241105 Lash Engineering, Inc. Civil/Consulting/Wastewater/Planning 1104 Cindy Carr Drive 7 Matthews,NC 28105 Phone: 704-847-3031 mikc1 ,LashEnginccring.com Lash Engineering, Inc. Engineers Report for: Payne's Court — Stormwater Narrative Alleghany County, NC. The project consists of 16 lots on a common cul-de-sac (Payne's Court). The lots will have a common wastewater drain field and be supplied with potable water by Aqua. The site boundaries encompass approximately 17.2 acres (750,363 sf.). The denuded area was along the ridge for about 170 feet on either side of Payne's Court-just enough to install the RV pads and a small cottage (about 6.5 ac.), however the Financial Responsibility form declared the entire site. At the bottom of the slope on the west side of the development about 400' from the street, is a 50-foot buffer along the unnamed Mitchell Creek tributary. The other side of Payne's Court drains to an unnamed tributary (drainage way) that drains down to the Mitchell River Basin "Waters of the Mitchell River". These creek outfalls are shown in the plans. Mitchell River is a "High Quality"watershed that requires extra measures for stormwater protection. This development falls within that watershed and is impacted by those protection regulations. There is approximately 1,075 sf(0.025 ac.) of surface waters from the on-site creek. This project is to be developed as a "Low Density" development. Under the Low-Density guidelines for developments a 12% threshold has been established for a non-coastal county, high quality water, and no stormwater controls. This development will incorporate those guidelines. The existing creeks and drainage ways are to remain undisturbed. There are no improvements within a 100' of the 50' buffer. The entire cul-de-sac will be accessed through one intersection. As stated before, the development occurs on top of a ridge that drains downhill on all three sides. Payne's Court is built along the ridge. The pavement is crowned so that stormwater is diverted to either side off the pavement and onto the grassed area that discharges the stormwater onto the slope that disperses it in a sheet to shallow flow fashion such that the grasses can remain stabilized. The houses have a roof gutter system with downspouts that are collected and piped down to the bottom of the ridge underground with 4" black corrugated HDP pipe and allowed to discharge at the bottom of the slope where the grade is flatter, and the discharge can disperse to sheet flow. Several dimensions were added to the plan to show areas left natural, undisturbed, grassed or wooded. The soils are Soils: Group III Clay Loam. The soil varies in slope from flat to steep. Summary: The road has been constructed, the RV pads have been installed and all but six (6) of the cottages have been built. The plans show these improvements, and a table of impervious areas shows the square footage for each lot. 0 Six cottages remain to be built. • All of the RV Pads have been accounted in the table. • There is no off-site drainage. The project is located on a ridge. • House gutters and downspouts are piped to the bottom of the ridge. • A total of 11,363 sf. is available to maximize the 12% threshold. • On a per lot basis this equates to 11,363/6= 1,890 sf. per cottage. • The maximum size cottage allowed by the approved&recorded HOA documents is 1,700 sf. • Assuming that there might be an additional 100 sf of porches & walks, the maximum impervious area per lot would be 1,800 sf. (This amount is shown on the plan). • 1,800 sf proposed is less than 1,890 sf. allowable so the project will be less than the 12% allowable impervious area. The 1,800 sf is shown in plan. • Therefore, the project is in compliance with the Low Density 12%requirement. The project is in compliance with the Low-Density guidelines for a 12% impervious allowance utilizing dispersed flow and no stormwater controls as a result of the Mitchell River watershed being designated as a"High Quality" stream. This is a non-coastal county. Please contact Lash Engineering, Inc. if you have any questions or concerns at (704)847- 3031. Michael Lash, PE.